1. Field of the Invention
The present invention relates to an optical pickup which utilizes coherent light for use in the field of optical information processing, and also to an optical disk apparatus incorporating the optical pickup.
2. Description of the Related Art
DVDs (digital video disks), which define one species of optical disks, can record 4.7 GB of data per disk medium with a diameter of 12 cm by utilizing a red semiconductor laser. Thus, signals equivalent to about 2 hours of motion pictures in the NTSC format can be recorded/reproduced on a single disk. A semiconductor laser which is employed as a light source in such a DVD apparatus typically generates red laser light with a wavelength of about 635 nm to about 650 nm, and has output power of about 5 mW. The relative intensity of noise (RIN) is generally xe2x88x92130 dB/Hz, thus satisfying the DVD requirement of xe2x88x92126 dB/Hz or smaller RIN.
However, the following problem may occur in a conventional DVD apparatus incorporating the above-described red semiconductor laser when reproducing motion pictures of the HDTV (high definition TV) class, which is one type of high quality TVs that requires high density recording/reproduction as necessitated by increase in the amount of information to be processed.
Specifically, the use of a red semiconductor laser, i.e., a semiconductor laser having a relatively long wavelength, as light source permits data equivalent to only about 40 minutes of motion pictures to be recorded on one DVD medium. Therefore, it is impossible to record or reproduce a relatively long program, e.g., a movie, on one disk. In addition, since the amount of information to be recorded/reproduced increases with the enhancement in the quality of images, a higher transfer rate may be required at the time of recording/reproduction. This calls for a great increase in the rotation speed of the disk.
The optical pickup of the present invention includes: a laser light source having an oscillating wavelength of 435 nm or less; an optical system providing light emitted from the laser light source with a prescribed optical path; and an optical detector for detecting light from the optical system, wherein the laser light source is provided with wavelength locking by optical feedback.
The laser light source may be a GaN type semiconductor laser.
The optical feedback of the laser light source may be provided by a grating structure.
In one embodiment, the laser light source is a semiconductor laser having a DBR structure, and the optical feedback thereof is provided by the DBR structure. The DBR structure may be formed in the vicinity of an end face opposite to a light emitting portion of the semiconductor laser. A member for absorbing laser light may be provided on an end face opposite to a light emitting portion of the semiconductor laser.
A tapered beam-shaping portion may be provided on the side of a light emitting portion of the laser light source.
The laser light source may be operated with RF superimposition.
According to another aspect of the present invention, the optical pickup includes: a laser light source; an optical system providing light emitted from the laser light source with a prescribed optical path; an optical detector for detecting light from the optical system; and a control member for controlling a light amount of an incident light onto the optical detector.
In one embodiment, the controlling member controls the light amount of the incident light onto the optical detector by controlling a polarization direction of the incident light.
Specifically, the controlling member may change a polarization direction of a laser light emitted from the laser light source, thereby controlling the polarization direction of the incident light onto the optical detector. For example, the laser light source may be a semiconductor laser, and the controlling member may apply pressure to the semiconductor laser, thereby changing the polarization direction of the laser light emitted from the semiconductor laser.
Alternatively,the controlling member may be a variable wavelength plate disposed between a polarizing optical element and a focus lens in the optical system.
The incident light onto the optical detector may be a signal light from an optical disk medium.
The optical disk apparatus according to the present invention includes: a laser light source having an oscillating wavelength of 435 nm or less; an optical system providing light emitted from the laser light source with a prescribed optical path; an optical detector for detecting light from the optical system; and an optical disk medium having pits with a length of 0.3 xcexcm or less, wherein the laser light source is provided with wavelength locking by optical feedback.
The laser light source may be a GaN type semiconductor laser.
The optical feedback of the laser light source may be provided by a grating structure.
In one embodiment, the laser light source is a semiconductor laser having a DBR structure, and the optical feedback thereof is provided by the DBR structure. The DBR structure may be formed in the vicinity of an end face opposite to a light emitting portion of the semiconductor laser. A member for absorbing laser light may be provided on an end face opposite to a light emitting portion of the semiconductor laser.
A tapered beam-shaping portion may be provided on the side of a light emitting portion of the laser light source.
The laser light source may be operated with RF superimposition.
Preferably, the laser light source is a semiconductor laser having a level of a relative intensity of noise (RIN) of xe2x88x92135 dB/Hz or less.
The apparatus may perform optical recording onto the optical disk medium by using the light emitted from the laser light source.
According to another aspect of the present invention, the optical disk apparatus includes: a laser light source; an optical system providing light emitted from the laser light source with a prescribed optical path; an optical detector for detecting light from the optical system; an optical disk medium having pits with a length of 0.3 xcexcm or less; and a control member for controlling a light amount of a signal light incident onto the optical detector from the optical disk medium.
In one embodiment, the controlling member controls the light amount of the signal by controlling a polarization direction of the signal light.
Specifically, the controlling member may change a polarization direction of a laser light emitted from the laser light source, thereby controlling the polarization direction of the signal light. For example, the laser light source may be a semiconductor laser, and the controlling member may apply pressure to the semiconductor laser, thereby changing the polarization direction of the laser light emitted from the semiconductor laser.
Alternatively, the controlling member may be a variable wavelength plate disposed between a polarizing optical element and a focus lens in the optical system.
Thus, the invention described herein makes possible the advantage of providing, in the implementation of an optical pickup and an optical disk apparatus utilizing a short-wavelength laser as a light source, a high-performance optical pickup capable of high-density recording/reproduction and an optical disk apparatus incorporating such an optical pickup.
The optical pickup according to the present invention, and the optical disk apparatus incorporating the same, utilize light having a relatively short wavelength, e.g., light of blue and other colors on the shorter end of the spectrum. As a result, it is possible to realize a high-performance, high definition DVD (HD-DVD) apparatus which is capable of recording/reproducing information in pits of an optical disk that are far more minute than those of an optical disk for a conventional DVD apparatus.
Furthermore, by performing wavelength locking of the semiconductor laser used as a light source, an optical pickup and an optical disk apparatus which are immune to returned light and capable of excellent recording/reproduction performance with a low noise level can be provided.
This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.